Method of making a hollow,fiber-reinforced plastic pressure vessel



n 1969 A. J. WILTSHIRE METHOD OF MAKING A HOLLOW, FIBER REINFORCEDPLASTIC PRESSURE VESSEL Filed May 16, 1966 FIG 2 INVENTOR. ARTHUR J.WILTSHIRE BY 7244/11 ATTORNEY United States Patent U.S. Cl. 156-69 9Claims ABSTRACT OF THE DISCLOSURE A filament winding technique forfabricating a hollowfilament-wound oblate, spheroidal pressure vessel. Aflexible, hollow thermoplastic liner having an oblate spheroidalexternal configuration is subjected to an internal pressure while theflattened poles of the liner are restrained. A rigid winding mandrel isthus provided and the restraint on the flattened poles prevents theliner from assuming a spherical shape. Resin-impregnated continuousfilaments are wound about the surface of the liner in a geodesicpattern. The restraint on the flattened poles of the liner is removed topermit the vessel to assume a neutral shape and the resin is then cured.

This invention relates to a method of fabricating a hollow,fiber-reinforced pressure vessel and, more particularly, to a method offabricating a hollow, fiber-reinforced, oblate, spheroidal pressurevessel having a filament-wound sidewall.

Filament-wound pressure vessels have been widely accepted as vessels forthe containment of pressurized fluid in those applications that requirehigh stress levels and low density, excellent corrosion, impact, andshatter resistance, and highly predictable burst and cyclecharacteristics. Filament-wound pressure vesselsare designed to takeadvantage of the high tensile strengths of certain filaments, such asglass fibers. Glass fibers have a modulus of 10x10 p.s.i. and a tensilestrength of x10 p.s.i. and, in order to take advantage of these physicalproperties, it is important to orient the fibers so that substantiallyall of these fibers are subjected to tensile loads.

Pressure vessels have been wound with filaments so that the tensileloads are carried by the filaments. The prior art filament windingtechniques involve winding the filament in a desired pattern about arigid mandrel to form the pressure vessel. The external surfaceconfiguration of the mandrel conforms to the final desired surfaceconfiguration of the pressure vessel. According to these prior arttechniques, the mandrel is formed from a fusible material, such as a lowmelting point metal or wax, which is removed from the interior of thewound pressure vessel by applying sufficient heat to melt the fusiblecore. Other mandrels have been molded from plaster of Paris and, afterthe winding and resin-curing steps, such mandrels are dissolved by asuitable fluid. It is often desirable to provide a filament-Woundpressure vessel having a thermoplastic liner to minimize leakage and toprovide corrosion resistance. Such liners are applied as a coating tothe rigid mandrel prior to the winding operation.

Although these winding operations have produced satisfactory pressurevessels, the step of removing the rigid mandrel is cumbersome andcomprises a major portion of the production time per pressure vessel. Itis, accordingly, an object of the present invention to provide a methodfor making a filament-wound pressure vessel which eliminates many of thecumbersome steps in prior art filament winding techniques.

It is a more particular object of this invention to provide a method formaking a hollow, fiber-reinforced plastic, oblate, spheroidal pressurevessel by winding 2. resin-impregnated filament onto a normally flexibleliner.

These objects are accomplished by providing a hollow, thermoplasticliner having an oblate, spheroidal, external configuration, andsubjecting the liner to an internal pressure while restraining theflattened poles of the liner to provide a rigid winding mandrel and toprevent the liner from assuming a spherical shape under its internalpressure. This rigid winding mandrel is then rotated about its polaraxis and resin-impregnated filaments are wound on the liner in ageodesic pattern by repeatedly orbiting the filaments to be wound in asingle, flat winding zone which passes through the geometric center ofthe liner. According to one aspect of this invention, the winding zoneis more nearly aligned with the polar axis than with a planeperpendicular to the polar axis. After the winding operation has beencompleted, the restraint on the poles is relaxed and the pressure isincreased so that the vessel will assume its true geometrical shape.Thereafter, the resin is cured to a rigid state.

These and other objects, features, and advantages of the invention willbecome more apparent from the following detailed description of thedrawings.

In the drawings:

FIG. 1 is an elevational view, partly in section, of a pressure vesselliner mounted on an arbor and about to be wound with a filament inaccordance with the teachings of this invention;

FIG. 2 is an elevational view of a pressure vessel produced inaccordance with the present invention; and

FIG. 3 is a cross sectional view of the pressure vessel, the plane ofthe section being indicated by the line 3-3 in FIG. 2.

Referring now to the drawings, a thermoplastic tank liner 10 isillustrated. The liner 10 may comprise a polypropylene shell having athickness of one-sixteenth inch. The liner 10 may be rotationally castor blow-molded into the approximate shape of the finished pressurevessel. The shape illustrated in an oblate spheroid having vertical,elliptical cross sections, with an ellipse ratio of 1.25:1.

The liner 10 is provided with fittings 11 and 12 at its flattened poles.These fittings may be cemented on or they may be molded into the linerwhen the liner is formed.

The liner 10 is mounted on an arbor 13 by inserting one end 13a of thearbor 13 first through a polar opening 15 and then through a polaropening 14, which openings are formed in the liner. One end of the arbor13 has an enlarged head portion 16 which is received by the opening 15.The head 16 carries an ()-ring 17 which pro vides a fluid-type sealbetween the head 16 and the opening 15. The head 16 is provided with anannular flange 18 which butts against the end of the opening 15. A cap19 is threaded onto the fitting 12 to lock the fitting and, therefore,the liner relative to the arbor 13.

A hollow plug 20 serves to restrain the opening 14 relative to the arbor13. The plug 20 includes a tapered, projecting end portion 21 which isreceived by the opening 14 and a threaded collar 22 which surrounds andthreadedly engages the fitting 11. A fluid-type seal is effected betweenthe plug 20 and the opening 14 and between an axial bore 23 of the plug20 and the arbor 13 by O-rings 24 and 25 respectively.

The plug 20 has a conical bore 26 and the conical bore 26 receives asplit taper clamp 27. The taper clamp 27 is provided with an axial bore28 which receives the arbor 13 and a tapered projecting end portion 29which is received by the conical bore 26. The end portion 29 is providedwith a plurality of radial slots 30 which permit the taper clamp totightly grip the arbor 13 as the clamp is wedged into the conical bore26. The clamp 27 is fixed to the plug 20 by bolts 31. The degree towhlch the bolts 31 are tightened determines the radial force exered onthe arbor 13 by the clamp 27.

The end 13a of the arbor 13 is journalled for rotation about its axis inan arm 32 of a conventional polar winding machine (not shown). Suchwinding machines include a winding arm 33 which is adapted to orbit theliner 10 at relatively high speed while the liner 10 is rotated aboutltS polar axis at a relatively low speed. The winding arm 33 is adaptedto orbit in a single plane designated by the plane P in FIG. 1. Thewinding plane P passes through the geometric center 6 of the liner 10.

After the liner has been mounted on the arbor 13 in the previouslydescribed manner, the interior of the liner is pressurized with asuitable fluid, such as air. There is provided a bore 34 through thehead 16 and the arbor 13 which communicates with the interior of thel1ner 10. A valve 35 is provided at the outer end of the bore 34 and isconnected to a suitable fluid pressure line to admlt pressure to theinterior of the liner 10. It should be noted that the liner 10 wouldtend to assume spherical shape upon being pressurized but, since thepoles of the liner 10 are restrained during the pressurizing step by theassembly, including the arbor 13, its head 16, the cap 1?, and the plug20, this tendency is obviated. The l1ner 10 is pressurized to, forexample, 10 p.s.i.g. so that it provides a rigid winding surface and,therefore, comprises a r1g 1d winding mandrel for the winding operation,WhlCh w1ll now be described.

A ribbon or band 36 sidewall of the liner 10 by attaching one end of theribbon or band to a portion of the liner 10, a portion of the fitting12, or a portion of the fitting 11, by a suitable cement, so that thatend portion straddles or is bisected by the plane of rotation P Theribbon or band 36 may be a single filament or, preferably, may comprisea predetermined number of glass fiber filaments or rovings which areimpregnated with a thermosetting resin, such as polyester resin, andgrouped together to form the band. Each roving comprises amultlplicityof ends which, in turn, lnclude a multlplicity of continuous glassfilaments. A number of ends 1n each roving varies with the type ofroving used, and the type and number of rovings employed in the processdepends upon the particular structural characteristics desired so thatthe finished pressure vessel has predictable burst characteristics. Theband 36 may be initially trained through a quantity of thermosettingresins and then trained through a resin stripper (not shown) so that theband has a resin to-glass-ratio of, for example 7:3 and 4:1.Alternately, the band may be preimpregnated with a predetermined amountof resin and then cured to its B state prior to the winding operation.

With one end of the band 36 attached to the l1ner 10, the fitting 12, orthe fitting 11 in the previously described manner, the winding operationproceeds. During the winding operation, the liner 10 is rotated aboutits polar axis at a relatively slow speed and the winding arm 33 isorbited about the liner 10 in the plane of rotation P The differentialbetween the speed of the arm 33 and the rotation of the liner 10determines the spacing between each turn of the band 36. The band 36,however, is wound onto the liner 10 in a single, flat winding zone W Thewidth of the winding zone W corresponds to the width of the band 36 andthe zone is bisected by the plane of rotation P The winding operationcontinues until one or more layers of filaments completely envelop theliner 10. After the liner has been completely wrapped with filaments,the unwound end of the band 36 is severed and cemented to the pressurevessel.

After the winding operation has been completed, the taper clamp 27 isremoved to permit the pressure vessel to assume a neutral shape. Thepressure in the liner 10 is increased to allow the vessel to assume itstrue geometric shape. This increased pressure is preferably about 10 iswound about the spheroidal percent of the burst strength of the vessel.The thermosetting resin is then cured by subjecting the pressure vesselto an elevated temperature of between approximately 200 and 300 -F. Sucha temperature tends to soften the thermoplastic liner so that asatisfactory bond is obtained between the resin-impregnated filamentsand the liner and, after such softening, the thermosetting resin curesto its rigid state. The pressure vessel is then permitted to cool toharden the thermoplastic liner and to produce a finished. pressurevessel. The heating and cooling steps are conducted While the pressurevessel is attached to the arbor 13, and with the taper clamp 27released, in order to ensure accurate alignment of the fittings 11 and12.

What is claimed is:

1. A method of fabricating a hollow, fiber-reinforced plastic, oblate,spheroidal pressure vessel, comprising the steps of providing aflexible, hollow, thermoplastic liner having an oblate, spheroidal,external configuration, subjecting said liner to an internal pressurewhile restraining the flattened poles of the liner to provide a rigidwinding mandrel and to prevent the liner from assuming a sphericalshape, Winding resin-impregnated continuous filaments about the surfaceof said liner in a geodesic pattern, removing the restraint on theflattened poles of the liner to permit the vessel to assume a neutralshape, and curing said resin.

2. A method of fabricating a hollow, fiber-reinforced plastic, oblate,spheroidal pressure vessel, comprising the steps of providing aflexible, hollow, thermoplastic liner having an oblate, spheroidal,external configuration, subjecting said liner to an internal pressurewhile restraining the flattened poles of the liner to provide a rigidwinding mandrel and to prevent the liner from assuming a sphericalshape, winding resin-impregnated continuous filaments about the surfaceof said liner in a geodesic pattern, removing the restraint on theflattened poles of the liner to permit the vessel to assume a neutralshape, increasing the internal pressure in said liner, and curing saidresin.

3. A method of fabricating a hollow, fiber-reinforced plastic pressurevessel, comprising the steps of providing a flexible, hollow,thermoplastic liner, subjecting said liner to an internal pressure whilerestraining said liner in an oblate shape to provide a rigid Windingmandrel, winding resin-impregnated continuous filaments about thesurface of said liner, removing the restraint on said liner, and curingsaid resin.

4. A method of fabricating a hollow, fiber-reinforced plastic pressurevessel, comprising the steps of providing a flexible, hollow,thermoplastic liner, subjecting said liner to an internal pressure whilerestraining said liner in an oblate shape to provide a rigid windingmandrel, winding resin-impregnated continuous filaments about thesurface of said liner, removing the restraint on said liner, increasingthe internal pressure in said liner, and curing said resin.

5. A method of fabricating a hollow, fiber-reinforced plastic, oblate,spheroidal pressure vessel, comprising the steps of providing aflexible, hollow liner having an oblate, spheroidal, externalconfiguration, subjecting said liner to an internal pressure whilerestraining the flattened poles of the liner to provide a rigid windingmandrel and to prevent the liner from assuming a spherical shape,impregnating continuous filaments with a thermosetting resin, rotatingsaid liner about its polar axis while winding said impregnated filamentson said liner in a geodesic pattern by repeatedly orbiting the filamentsto be wound in a single, fiat winding zone passing through the geometriccenter of said liner, said winding zone being more nearly aligned withsaid polar axis than with a plane perpendicular to said polar axis,removing the restraint on the flattened poles of the liner to permit thevessel to assume a neutral shape, curing said resin, and relieving theinternal pressure.

6. A method of fabricating a hollow, fiber-reinforced plastic, oblate,spheroidal pressure vessel, comprising the steps of providing aflexible, hollow liner having an oblate, spheroidal, externalconfiguration, subjecting said liner to an internal pressure whilerestraining the flattened poles of the liner to provide a rigid windingmandrel and to prevent the liner from assuming a spherical shape,impregnating continuous filaments With a thermosetting resin, rotatingsaid liner about its polar axis while winding said impregnated filamentson said liner in a geodesic pattern by repeatedly orbiting the filamentsto be wound in a single, flat winding zone passing through the geometriccenter of said liner, said winding zone being more nearly aligned withsaid polar axis than with a plane perpendicular to said polar axis,removing the restraint on the flattened poles of the liner to permit thevessel to assume a neutral shape, increasing the internal pressure insaid liner, curing said resin, and relieving the internal pressure.

7. A method of fabricating a hollow, fiber-reinforced plastic, oblate,spheroidal pressure vessel, comprising the steps of providing aflexible, hollow, thermoplastic liner having an oblate, spheroidal,external configuration, subjecting said liner to an internal pressureWhile restraining the flattened poles of the liner to provide a rigidwinding mandrel and to prevent the liner from assuming a sphericalshape, impregnating continuous filaments with a thermosetting resin,rotating said liner about its polar axis while winding said impregnatedfilaments on said liner in a geodesic pattern by repeatedly orbiting thefilaments to be wound in a single, flat Winding zone passing through thegeometric center of said liner, said winding zone being more nearlyaligned with the polar axis than with a plane perpendicular to saidpolar axis, removing the restraint on the flattened poles of the linerto permit the vessel to assume a neutral shape, heating the wound vesselto soften said liner, to fuse said liner to said continuous filaments,and to cure said resin, and relieving the internal pressure in saidvessel.

8. A method of fabricating a hollow, fiber-reinforced plastic, oblate,spheroidal pressure vessel, comprising the steps of providing aflexible, hollow, thermoplastic liner having an oblate, spheroidal,external configuration, sub- 'ecting said liner to an internal pressurewhile restraining the flattened poles of the liner to provide a rigidwinding mandrel and to prevent the liner from assuming a sphericalshape, impregnating continuous filaments with a thermosetting resin,rotating said liner about its polar axis while winding said impregnatedfilaments on said liner in a geodesic pattern by repeatedly orbiting thefilaments to be wound in a single, flat Winding zone passing through thegeometric center of said liner, said winding zone being more nearlyaligned with the polar axis than with a plane perpendicular to saidpolar axis, removing the restraint on the flattened poles of the linerto permit the vessel to assume a neutral shape, increasing the internalpressure in said liner, heating the Wound vessel to soften said liner,to fuse said liner to said continuous filaments, and to cure said resin,and relieving the internal pressure in said vessel.

9. The method according to claim 8 wherein said liner is subjected to aninitial internal pressure of about 10 p.s.i. gauge and wherein theincreased internal pressure is approximately ten percent of the burststrength of the completed pressure vessel.

References Cited UNITED STATES PATENTS 3,057,509 10/1962 Bernd.3,282,757 11/1966 Brussee 15669 3,210,228 10/1965 Bluck 156173 XR3,137,405 6/1964 Gorcey 220-3 3,047,191 7/ 1962 Young.

EARL M. BERGERT, Primary Examiner. PHILIP DIER, Assistant Examiner.

US. Cl. X.R.

